Fire resistant glazings / Pilkington Group Limited

Title: Fire resistant glazings.Abstract: An additive for alkali metal silicate solutions, comprising a quaternary ammonium compound having the general formula (1) R1R2R3R4N+OH−, wherein R1, R2, R3 and R4 which may be the same or different represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups, hydroxy-substituted alkaryl groups comprising from 1 to 12 carbon atoms, or groups having the general formula —[CH2]n-N+R5R6R7 wherein n is an integer having a value of from 1 to 12, the group —[CH2]n may be hydroxy-substituted, and R5, R6 and R7 which may be the same or different represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups or hydroxy-substituted alkaryl groups comprising from 1 to 12 carbon atoms; with the proviso that at least one of the groups R1, R2, R3, R4, R5, R6 and R7 represents a hydroxy-substituted alkyl group or a hydroxy-substituted alkaryl group comprising at least 2 carbon atoms wherein the hydroxy substituent is not located on a carbon atom which is bonded to a nitrogen atom. ...

This invention relates to fire resistant glazings, interlayers useful in such glazings, solutions useful in the production of these interlayers, additives useful in the preparation of said solutions, and methods of directing and/or stabilising the diversity and/or distribution of silicate structures in said solutions.

Fire resistant glazings comprising at least one interlayer comprising a silicate waterglass and at least two panes of glass are well known. When these laminates are exposed to a fire, the interlayer intumesces and expands to form a foam. The foam helps to maintain the integrity of the glazing thereby restricting the spread of a fire and also provides a thermally insulating layer which acts as a barrier to infra-red radiation. These glazings can meet the requirements of most applicable building regulations and are widely used in architecture and building.

In order to be useful, the interlayers must be optically clear and retain that clarity throughout the lifetime of the glazing. They must also provide the required degree of fire resistance. Interlayers which comprise a higher proportion of silica impart a higher degree of fire resistance to the glazing but are more difficult to manufacture as optically clear materials.

The interlayers may be manufactured using a variety of processes. The most widely used process involves pouring a silicate waterglass solution onto the surface of a glass pane and drying that solution under carefully controlled conditions. Such processes are described for example in GB 1518958, GB 2199535, U.S. Pat. No. 4,451,312, U.S. Pat. No. 4,626,301 and U.S. Pat. No. 5,766,770. A variant upon this process in which a silicate solution is dried upon a flat surface to form a film which can be separated from that surface and used as an interlayer is described in WO 01/70495. EP 620781 describes a process in which a silicate solution is poured into the space between two opposed glass panes and allowed to self cure to form a fire resistant glazing.

Whatever the method by which they are produced these silicate based interlayers and the waterglass solutions from which they are produced comprise a plurality of silicate anions. The precise composition of the interlayers and thereby their properties, varies with the conditions under which they are produced. The nature of silicate structures in solution may be thought of as silicon surrounded by oxygen in an almost regular tetrahedron. Pure silicic acid, Si(OH)4, however, does not exist in solution. Condensation reactions occur between such units giving rise to silioxane (Si—O—Si) bridges. The silicon-oxygen tetrahedra may therefore share a corner which, in turn, gives rise to a wide variety of silicate structures in solution.

In order to describe such structures it is convenient to adopt the ‘Q’ nomenclature used by Engelhardt et al. (G. Engelhardt and O. Rademacher, J. Mol. Liquids, 1984, 27, 125). The “Q-unit” (for quadrifunctional) represents a SiO4 group with the number of other Q-units directly attached to the one under consideration, indicated by a superscript. Taking the example of the condensation reaction mentioned above, the silicic acid species would be denoted as a Q0 species as the silicon has no siloxane bridges to any other silicon atoms. The dimer formed from the condensation reaction however, would be denoted as Q12 as each silicon atom is bonded to one other via a siloxane bridge. Additional condensation reactions give rise to a wide variety of silicate structures, groups of which may be assigned a Q number and hence easily referred to.

A need exists to improve the mechanical properties of silicate interlayers particularly in the elastomeric range of silicate materials. Currently, silicate interlayers are brittle and therefore difficult to handle and cannot be manipulated. Accordingly, a need exists for a silicate solution that has the potential to dry or cure to form a flexible film. It would also be beneficial to control to varying degrees the structural homogeneity of silicate interlayers, thereby controlling cohesion and water distribution throughout the interlayers.

According to a first aspect of the present invention there is provided an additive for alkali metal silicate solutions, comprising a quaternary ammonium compound having the general formula 1

R1R2R3R4N+OH− (1)

wherein R1, R2, R3 and R4 which may be the same or different represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups, hydroxy-substituted alkaryl groups comprising from 1 to 12 carbon atoms, or groups having the general formula —[CH2]n-N+R5R6R7 wherein n is an integer having a value of from 1 to 12, the group —[CH2]n- may be hydroxy-substituted, and R5, R6 and R7 which may be the same or different represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups or hydroxy-substituted alkaryl groups comprising from 1 to 12 carbon atoms;
with the proviso that at least one of the groups R1, R2, R3, R4, R5, R6 and R7 represents a hydroxy-substituted alkyl group or a hydroxy-substituted alkaryl group comprising at least 2 carbon atoms wherein the hydroxy substituent is not located on a carbon atom which is bonded to a nitrogen atom.

The above mentioned additives for silicate solutions serve to impart a degree of control on the structural homogeneity of silicate interlayers prepared using said solutions, and thereby enable the control of the properties of those interlayers and/or of fire resistant glazings comprising those interlayers. It has surprisingly been found that the above additives can be specifically designed to direct and/or stabilise desired diversity and/or distribution of silicate structures in alkali metal silicate solutions and corresponding dried or cured interlayers. This enables the properties of fire resistant interlayers such as cohesion, flexibility, water distribution to be tailored to suit particular needs by controlling the structural homogeneity of said interlayers. This invention also provides improved thermal stability and ageing performance of said interlayers.

It has been determined that the nature and magnitude of these structure directing effects (SDEs) are directly related to the length of the alkyl chains and the frequency of hydroxy substituents in the additives. Namely, the addition to alkali metal silicate solutions of additives with longer alkyl chains results in a greater diversity and/or distribution of silicate structures in the solution. However, this effect can be counteracted by an increased number of hydroxy substituents in the additives which enables said additives to direct and/or stabilise the diversity and/or distribution of silicate structures in alkali metal silicate solutions. These two effects can be utilised in tandem to fine tune the properties of alkali metal silicate solutions and interlayers prepared from said solutions.

The occurrence of aromatic substituents has a somewhat similar silicate SDE to that of alkyl chains in that diversity and distribution is increased. However, the SDEs of aromatic substituents in the additives differ from those of alkyl groups in that aromatic substituents do not favour smaller silicate structures (Q0 to Q23). Aromatic substituents do not direct towards monodisperse solutions, but do direct towards larger silicate species (larger than Q23), whereas alkyl groups are not as selective in their control of diversity and distribution.

It has been found that an increase in the temperature of alkali metal silicate solutions will generally result in a partial shift in the dynamic equilibrium and consequently an increase in the diversity and/or distribution of the silicate structures contained therein. Accordingly, this effect can be detrimental in cases where less diversity and a narrower distribution are desired. However, the use of the above additives can retard or remove this effect of an increase in temperature, so that the diversity and/or distribution of silicate structures in the solution are not affected. Therefore, the additives are useful for stabilising silicate structures in alkali metal silicate solutions that require heating, for instance when alkali metal silicate solutions are heated upon drying or curing to form an interlayer.

Furthermore, it has been determined that an interlayer obtained from the drying or curing of an alkali metal silicate solution comprises fewer of the smaller Qn silicate structures present in the solution, suggesting that such structures undergo condensation reactions upon drying or curing resulting in larger Qn structures. This effect can be exploited when using the additives of this invention because the SDEs of the additives can be utilised to eliminate smaller Qn structures prior to drying or curing, enabling the formation of larger Qn silicate structures, in a greater proportion and/or more controlled manner than could normally be obtained in the resultant interlayers.

At least one, at least two or at least three of the groups R1, R2, R3 and R4 may represent groups having the general formula —[CH2]n-N+R5, R6, R7 wherein n is an integer having a value of from 1 to 12, the group —[CH2]n- may be hydroxy-substituted, and R5, R6 and R7 which may be the same or different represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups or hydroxy-substituted alkaryl groups comprising from 1 to 12 carbon atoms.

In some embodiments at least two, preferably at least three, more preferably at least four of the groups R1, R2, R3, R4, R5, R6 and R7 represent a hydroxy-substituted alkyl group or a hydroxy-substituted alkaryl group comprising at least 2 carbon atoms wherein the hydroxy substituent is not located on a carbon atom which is bonded to a nitrogen atom.

R1, R2, R3 and R4 which may be the same or different may represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups, or hydroxy-substituted alkaryl groups comprising from 1 to 8 carbon atoms, preferably from 1 to 6 carbon atoms, more preferably from 1 to 4 carbon atoms. In some embodiments, R1, R2, R3 and R4 which may be the same or different may represent alkyl groups, hydroxy-substituted alkyl groups, alkaryl groups, or hydroxy-substituted alkaryl groups comprising from 3 to 8 carbon atoms, preferably from 3 to 6 carbon atoms, more preferably 3 or 4 carbon atoms.

At least one of the groups R1, R2, R3 or R4 may represent a group having the general formula —[CH2]n-N+R5, R6, R7 wherein n is an integer having a value of from 1 to 8, preferably a value of from 1 to 6, more preferably a value of from 1 to 4.

A preferred group of compounds having the general formula 1 are those which comprise at least two hydroxy substituents, preferably at least three hydroxy substituents, more preferably at least four hydroxy substituents, even more preferably at least five hydroxy substituents.

At least two of the groups R1-7 may be hydroxy substituted, preferably at least three of the groups R1-7 are hydroxy substituted, more preferably at least four of the groups R1-7 are hydroxy substituted, even more preferably at least five of the groups R1-7 are hydroxy substituted.

At least one of the groups R1-7 may comprise at least two hydroxy substituents, preferably at least three hydroxy substituents, more preferably at least four hydroxy substituents.

The hydroxy substituents may each be located upon different carbon atoms. Without wishing to be bound by any theory the applicants believe that the separation of the hydroxyl substituents contributes to the stability and order which they confer upon the silicate solution.

When at least one of the groups R1, R2, R3 or R4 represents a group having the general formula —[CH2]n-N+R5R6R7, and each nitrogen is substituted with two methyl groups, the group —[CH2]n- may be hydroxy substituted. When the groups R1-3 are —C2H4OH groups, R4 may be —CH2OH, or a hydroxy-substituted or hydroxy-unsubstituted alkyl or alkaryl group comprising from 2 to 12 carbon atoms.

When the groups R1 and R2 are both —C2H4OH groups, R3 and R4 which may be the same or different may be a hydroxy-substituted or hydroxy-unsubstituted alkyl or alkaryl group comprising from 1 to 12 carbon atoms, provided that when R3 and R4 comprise 2 carbon atoms each, at least one of R3 and R4 is hydroxy-substituted.

These additives may conveniently be synthesised by the reaction of a tertiary amine having the general formula R1R2R3N with an alkyl halide having the general formula R4Z, wherein Z represents a halogen atom, to form a tetraalkyl ammonium halide. This halide can be converted to the corresponding hydroxide using an anion exchange resin.

The product of these syntheses is an aqueous solution of the quaternary ammonium compound. The concentration of this solution will generally be in the range 20% wt to 50% wt of solid material. Such a solution may be readily mixed with an aqueous solution of an alkali metal silicate waterglass.

According to another aspect the present invention provides a stable aqueous solution for the production of fire resistant glazings comprising:

at least one alkali metal silicate,
at least one additive in accordance with the first aspect of the present invention, and water.

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